Exhaust purification device of internal combustion engine, and control method thereof

ABSTRACT

An exhaust purification device includes a particulate filter ( 10 ), an air flow meter ( 7 ) that detects the amount of fresh air flowing in an intake passageway ( 3 ), and an EGR device ( 30 ) that supplies gas to a site in the intake passageway ( 3 ) between the air flow meter ( 7 ) and the particulate filter ( 10 ). The exhaust purification device detects the amount of flow of exhaust passing through the particulate filter on the basis of the amount of gas supplied by the EGR device ( 30 ), and the intake air amount detected by the air flow meter (S 108 ), and detects the differential pressure between the upstream side and the downstream side of the particulate filter, and determines whether the particulate filter is clogged on the basis of the amount of flow and the differential pressure of exhaust (S 110 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an exhaust purification device of an internalcombustion engine and a control method thereof.

2. Description of the Related Art

In an exhaust purification device of an internal combustion engineequipped with an EGR (exhaust gas recirculation) passageway thatconnects an exhaust passageway downstream of a particulate filter and anintake passageway downstream of an air flow meter, a technology thatdetermines the presence/absence of the clogging of the particulatefilter on the basis of the differential pressure between the upstreamside and the downstream side of the particulate filter is disclosed inJapanese Patent Application Publication No. JP-A-2005-69207.

However, if the degree of opening of an EGR valve provided in an EGRpassageway is changed, the amount of exhaust that passes through theparticulate filter changes. Therefore, the differential pressure betweenthe upstream side and the downstream side of the particulate filterchanges, so that there is a possibility of error in the determinationregarding the clogging of the particulate filter.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a technology capable of moreaccurately determining the presence/absence of the clogging of aparticulate filter in an exhaust purification device of the internalcombustion engine.

An exhaust purification device of an internal combustion engineaccording to a first aspect of the invention includes: a particulatefilter that is provided in an exhaust passageway and that traps aparticulate matter in exhaust; intake air amount detection means fordetecting an amount of fresh air flowing in an intake passageway; gassupply means for supplying a gas to the intake passageway that is on adownstream side of the intake air amount detection means and on anupstream side of the particulate filter; exhaust flow calculation meansfor calculating an amount of flow of exhaust passing through theparticulate filter based on the amount of the gas supplied and theamount of fresh air detected; differential pressure detection means fordetecting a differential pressure between the upstream side and thedownstream side of the particulate filter in the exhaust passageway; andclogging determination means for determining whether the particulatefilter is clogged based on the amount of flow of exhaust calculated andthe differential pressure detected.

In the first aspect, there is a correlation between the amount of flowof exhaust passing through the particulate filter, the amount of freshair detected by the intake air amount detection means, and the amount ofgas supplied by the gas supply means. For example, as the amount offresh air decreases, the amount of flow of exhaust also decreases.Besides, for example, as the amount of gas supplied by the gas supplymeans decreases, the amount of flow of exhaust decreases. From theforegoing relationship, the exhaust flow calculation means calculatesthe amount of flow of exhaust passing through the particulate filter onthe basis of the amount of gas supplied by the gas supply means and theintake air amount detected by the intake air amount detection means.

In the first aspect, when the particulate filter traps particulatematter, the passage resistance against exhaust passing through theparticulate filter becomes greater. Therefore, there is a correlationbetween the differential pressure between the upstream side and thedownstream side of the particulate filter detected by the differentialpressure detection means, and the amount of particulate matter trappedon the particulate filter. Besides, when the passage resistance againstexhaust passing through the particulate filter becomes greater, theamount of flow of exhaust passing through the particulate filterdecreases, and therefore the differential pressure detected by thedifferential pressure detection means becomes smaller. From theserelationship, the clogging determination means determines whether theparticulate filter is clogged on the basis of the amount of flow ofexhaust calculated by the exhaust flow calculation means, and thedifferential pressure detected by the differential pressure detectionmeans.

As for the aforementioned clogging determination, it may also bedetermined whether or not the clogging has occurred in the particulatefilter, and the amount of particulate matter trapped on the particulatefilter may be estimated.

In the exhaust purification device of the internal combustion engine inaccordance with the foregoing first aspect, the gas supply means may bean EGR device that has an EGR passageway that connects the exhaustpassageway downstream of the particulate filter and the intakepassageway downstream of the intake air amount detection means, and anEGR valve that is provided in the EGR passageway and that changes apassageway cross-sectional area of the EGR passageway. The amount of thegas supplied by the gas supply means may be the amount of an EGR gasdetected by EGR gas amount detection means for detecting the amount ofthe EGR gas flowing in the EGR passageway.

In the foregoing aspect, when the amount of the EGR gas flowing in theEGR passageway is changed by operating the EGR valve, the amount of flowof exhaust passing through the particulate filter correspondinglychanges. The value obtained by summing the EGR gas amount flowing in theEGR passageway and the amount of fresh air is the amount of flow ofexhaust passing through the particulate filter. Specifically, theexhaust flow calculation means calculates the amount of flow of exhaustpassing through the particulate filter on the basis of the amount of theEGR gas detected by the EGR gas amount detection means, and the amountof fresh air detected by the intake air amount detection means.

Besides, since the amount of flow of exhaust passing through theparticulate filter and the differential pressure between upstream sideand the downstream side of the particulate filter have a correlationwith the amount of particulate matter trapped on the particulate filter,the knowledge of the amount of flow of exhaust and the differentialpressure allows the detection of the clogging of the particulate filter.

In the foregoing aspect, the exhaust purification device may furtherinclude a turbocharger that has a turbine in the exhaust passageway, anda compressor in the intake passageway. The EGR passageway may be alow-pressure EGR passageway that connects the exhaust passagewaydownstream of the turbine and the intake passageway upstream of thecompressor.

The pressure in the exhaust passageway downstream of the turbine isclose to the atmospheric pressure although it is higher than theatmospheric pressure. Besides, the pressure in the intake passagewayupstream of the compressor is lower than the atmospheric pressure.Therefore, the pressure of the EGR gas flowing in the low-pressure EGRpassageway is low in comparison with the case where the exhaustpassageway upstream of the turbine and the intake passageway downstreamof the compressor are connected.

In the case where the EGR gas flows in the low-pressure EGR passageway,the amount of exhaust combining the amount of the EGR gas and the amountfresh air passes through the particulate filter. In this case, too, theclogging of the particulate filter can be detected according to theforegoing aspect.

In the foregoing aspect, the EGR gas amount detection means may detectthe amount of flow of gas in the low-pressure EGR passageway from atleast the differential pressure between the passageway on the upstreamside of the EGR valve and the passageway on the downstream side of theEGR valve, and a degree of opening of the EGR valve.

In the foregoing aspect, when it is determined by the cloggingdetermination means whether the particulate filter is clogged, thedegree of opening of the EGR valve may be made smaller than when it isnot determined whether the particulate filter is clogged.

If the degree of opening of the EGR valve is made smaller, the EGR gasamount decreases. Therefore, the amount of flow of exhaust passingthrough the particulate filter approaches the amount of fresh air. Thismakes it possible to decrease the effect that the EGR gas has on theamount of flow of exhaust passing through the particulate filter, sothat the accuracy of the clogging determination can be improved.Furthermore, by fully closing the EGR valve, the amount of fresh air andthe amount of flow of exhaust become equal, so that the accuracy of theclogging determination can be further improved.

In the foregoing aspect, when the clogging determination meansdetermines whether the particulate filter is clogged, the degree ofopening of the EGR valve may be fixed.

If the degree of opening of the EGR valve changes, the amount of flow ofexhaust passing through the particulate filter changes. Due to this,there is possibility of making an error in the determination regardingthe clogging by the clogging determination means. According to theforegoing aspect, by fixing the degree of opening of the EGR valve, thefluctuation in the EGR gas amount flowing in the EGR passageway can berestrained, and therefore the accuracy of the clogging determination canbe improved. Incidentally, when the degree of opening of the EGR valveis fixed, it may be fixed in the fully closed state.

In the foregoing aspect, the exhaust purification device may furtherinclude a high-pressure EGR passageway that connects the exhaustpassageway upstream of the particulate filter and the intake passagewaydownstream of the intake air amount detection means, and a high-pressureEGR valve that changes the passageway cross-sectional area of thehigh-pressure EGR passageway. If the amount of the EGR gas flowing inthe EGR passageway is changed when the clogging determination meansdetermines whether the particulate filter is clogged, the EGR gas amountflowing in the high-pressure EGR passageway may be changed by thehigh-pressure EGR valve so that the EGR gas amount supplied into acylinder of the internal combustion engine is constant.

If the amount of EGR gas flowing in the EGR passageway is decreased, theaccuracy of the clogging determination can be improved, but the EGR gasamount supplied into the cylinder decreases. However, if the EGR gas iscaused to flow into the high-pressure EGR passageway so as to compensatefor the decrease in the amount of EGR gas flowing in the EGR passageway,the EGR gas amount supplied into the cylinder can be kept constant. Thismakes it possible to restrain, for example, the generation of NOx.

In the foregoing aspect, when it is determined by the cloggingdetermination means whether the particulate filter is clogged, the EGRvalve may be set at a degree of opening that is not the fully closedstate. The exhaust flow calculation means may estimate the amount offlow of exhaust passing through the particulate filter based on theamount of fresh air detected by the intake air amount detection meansand the amount of the EGR gas detected by the EGR gas amount detectionmeans, and the clogging determination means may determine whether theparticulate filter is clogged based on the amount of flow of exhaustestimated by the exhaust flow calculation means and the differentialpressure detected by the differential pressure detection means.

If the degree of opening of the EGR valve changes, the EGR gas amountflowing in the EGR passageway also changes. However, even in the casewhere the degree of opening of the EGR valve is changing with the elapseof time, the current amount of flow of exhaust can be determined as thecurrent amount of fresh air and an estimated EGR gas amount providedthat the EGR gas amount can be estimated from one moment to another. Dueto this, even when the amount of EGR gas fluctuates because the degreeof opening of the EGR valve is not fixed, the clogging determination onthe particulate filter can be performed with good accuracy.

In the foregoing aspect, determination by the clogging determinationmeans as to whether the particulate filter is clogged may be performedwhen at least one of (i) a condition that the internal combustion engineis in a steady state, (ii) a condition that temperature of theparticulate filter is within a predetermined range, and (iii) acondition that the vehicle has traveled a predetermined distance, ismet.

The exhaust purification device of the internal combustion engine inaccordance with the foregoing aspect is able to more accurately performthe clogging determination on the particulate filter.

A control method of an exhaust purification device of an internalcombustion engine according to a second aspect of the invention is foran exhaust purification device of an internal combustion engine thatincludes: a particulate filter that is provided in an exhaust passagewayand that traps a particulate matter in exhaust; intake air amountdetection means for detecting an amount of fresh air flowing in anintake passageway; gas supply means for supplying a gas to the intakepassageway that is on a downstream side of the intake air amountdetection means and on an upstream side of the particulate filter; anddifferential pressure detection means for detecting a differentialpressure between the upstream side and the downstream side of theparticulate filter in the exhaust passageway. In the control method ofthe exhaust purification device of the internal combustion engine, anamount of flow of exhaust passing through the particulate filter iscalculated based on the amount of the gas supplied and the amount offresh air detected, and it is determined whether the particulate filteris clogged based on the amount of flow of exhaust calculated and thedifferential pressure detected.

In the control method according to the second aspect, the gas supplymeans may be an EGR device that has an EGR passageway that connects theexhaust passageway downstream of the particulate filter and the intakepassageway downstream of the intake air amount detection means, an EGRvalve that is provided in the EGR passageway and that changes apassageway cross-sectional area of the EGR passageway, and EGR gasamount detection means for detecting an amount of an EGR gas flowing inthe EGR passageway. The amount of the gas supplied by the gas supplymeans may be the amount of the EGR gas detected by the EGR gas amountdetection means. The present invention also concerns an exhaustpurification device of an internal combustion engine which comprises aparticulate filter provided in an exhaust passageway and that traps aparticulate matter in exhaust; an intake air amount detection portionthat detects an amount of fresh air flowing in an intake passageway; agas supply portion that supplies a gas to the intake passageway that ison a downstream side of the intake air amount detection portion and onan upstream side of the particulate filter; an exhaust flow calculationportion that calculates an amount of flow of exhaust passing through theparticulate filter based on the amount of the gas supplied and theamount of fresh air detected; a differential pressure detection portionthat detects a differential pressure between the upstream side and thedownstream side of the particulate filter in the exhaust passageway; anda clogging determination portion that determines whether the particulatefilter is clogged based on the amount of flow of exhaust calculated andthe differential pressure detected.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and/or further objects, features and advantages of theinvention will become more apparent from the following description ofexample embodiments with reference to the accompanying drawings, inwhich the same or corresponding portions are denoted by the samereference numerals and wherein:

FIG. 1 is a diagram schematically showing an overall construction of aninternal combustion engine and its intake-exhaust system to which anexhaust gas purification device of an internal combustion engine inaccordance with an embodiment of the invention is applied;

FIG. 2 is a flowchart showing the flow of determination regardingparticulate filter clogging according to a first embodiment of theinvention;

FIG. 3 is a flowchart showing the flow of determination regardingparticulate filter clogging according to a second embodiment of theinvention;

FIG. 4 is a flowchart showing the flow of determination regardingparticulate filter clogging according to a third embodiment of theinvention; and

FIG. 5 is another flowchart showing the flow of determination regardingparticulate filter clogging according to a third embodiment of theinvention.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

Example embodiments of the exhaust purification device of an internalcombustion engine in accordance with the invention will be describedhereinafter with reference to the drawings.

i. First Embodiment

An internal combustion engine 1 shown in FIG. 1 is a water-cooledfour-stroke diesel engine that has four cylinders 2.

An intake pipe 3 and an exhaust pipe 4 are connected to the internalcombustion engine 1. An intermediate portion of the intake pipe 3 isprovided with a compressor housing 5 a of a turbocharger 5 that actsusing energy of exhaust as a drive source. The intake pipe 3 upstream ofthe compressor housing 5 a is provided with a first throttle 6 thatadjusts the amount of flow of intake flowing in the intake pipe 3. Thefirst throttle 6 is opened and closed by an electric actuator. Theintake pipe 3 upstream of the first throttle 6 is provided with an airflow meter 7 that outputs a signal that is in accordance with the amountof flow of intake flowing in the intake pipe 3. The intake air amount ofthe internal combustion engine 1 is measured by the air flow meter 7. Inthis embodiment, the air flow meter 7 corresponds to intake air amountdetection means in the invention.

The intake pipe 3 downstream of the compressor housing 5 a is providedwith an intercooler 8 that performs heat exchange between the intake andexternal air. The intake pipe 3 downstream of the intercooler 8 isprovided with a second throttle 9 that adjust the amount of flow ofintake flowing in the intake pipe 3. The second throttle 9 is opened andclosed by an electric actuator.

On the other hand, an intermediate portion of the exhaust pipe 4 isprovided with a turbine housing 5 b of the turbocharger 5. The exhaustpipe 4 downstream of the turbine housing 5 b is provided with aparticulate filter (hereinafter, simply referred to as “filter”) 10. Astorage reduction type NOx catalyst (hereinafter, simply referred to as“NOx catalyst”) is supported on the filter 10. This filter trapsparticulate matter in exhaust. The NOx catalyst stores oxides ofnitrogen (NOx) from exhaust when the oxygen concentration in the exhaustflowing into the NOx catalyst is high, and releases stored NOx when theoxygen concentration in the exhaust flowing into the NOx catalyst hasdropped. On the occasion, if a reducing component, such as hydrocarbon(HC), carbon monoxide (CO), etc., is present in the exhaust, the NOxreleased from the NOx catalyst is reduced. In this description, the term“storage (or store)” is used in the meaning of holding a substance(solid, liquid, gas molecules) in at least one of the manners thatinclude adsorption, adhesion, absorption, trapping, occlusion, etc.

A differential pressure sensor 11 that measures the pressure differencebetween the upstream side and the downstream side of the filter 10 isattached to the filter 10. The amount of particulate matter(hereinafter, referred to also as “PM”) deposited on the filter 10 canbe detected by the differential pressure sensor 11. In this embodiment,the differential pressure sensor 11 corresponds to differential pressuredetection means in the invention. In the exhaust pipe 4 downstream ofthe filter 10, an exhaust temperature sensor 12 that detects thetemperature of the exhaust flowing in the exhaust pipe 4 is attached.The temperature of the filter 10 is detected by the exhaust temperaturesensor 12.

The internal combustion engine 1 is equipped with a low-pressure EGRdevice 30 that recirculates a portion of the exhaust that flows in theexhaust pipe 4, to the intake pipe 3 at low pressure. The low-pressureEGR device 30 has a low-pressure EGR passageway 31, a low-pressure EGRvalve 32, and an EGR cooler 33. The low-pressure EGR passageway 31connects the exhaust pipe 4 on the downstream side of the filter 10 andthe intake pipe 3 that extends upstream of the compressor housing 5 aand downstream of the first throttle 6. Via the low-pressure EGRpassageway 31, exhaust is recirculated at low pressure. In thisembodiment, the exhaust recirculated via the low-pressure EGR passageway31 is termed low-pressure EGR gas. Besides, the amount of low-pressureEGR gas that flows through the low-pressure EGR passageway 31 isadjusted by adjusting the passageway cross-sectional area of thelow-pressure EGR passageway 31 with changes in the degree of opening ofthe low-pressure EGR valve 32. The EGR cooler 33 drops the temperatureof low-pressure EGR gas by causing heat exchange between thelow-pressure EGR gas passing through the EGR cooler 33 and cooling waterof the internal combustion engine 1. In this embodiment, thelow-pressure EGR device 30 corresponds to gas supply means in theinvention.

The internal combustion engine 1 is also equipped with a high-pressureEGR device 40 that recirculates a portion of the exhaust that flows inthe exhaust pipe 4, to the intake pipe 3 at high pressure. Thishigh-pressure EGR device 40 has a high-pressure EGR passageway 41, and ahigh-pressure EGR valve 42. The high-pressure EGR passageway 41 connectsthe exhaust pipe 4 on the upstream side of the turbine housing 5 b andthe intake pipe 3 downstream of the second throttle 9. Via thehigh-pressure EGR passageway 41, exhaust is recirculated at highpressure. In this embodiment, the exhaust recirculated via thehigh-pressure EGR passageway 41 is termed high-pressure EGR gas. As thepassageway cross-sectional area of the high-pressure EGR passageway 41changes with changes in the degree of opening of the high-pressure EGRvalve 42, the amount of high-pressure EGR gas that flows through thehigh-pressure EGR passageway 41 is adjusted.

An exhaust pressure sensor 13 that detects the pressure of exhaust isattached to the exhaust pipe 4 between the turbine housing 5 b and thefilter 10.

The internal combustion engine 1 constructed as described above isprovided with an ECU 20 that is an electronic control unit forcontrolling the internal combustion engine 1. This ECU 20 controls thestate of operation of the internal combustion engine 1 in accordancewith the operation condition of the internal combustion engine 1 and adriver's request. Besides the aforementioned sensors, an acceleratoroperation amount sensor 15 that outputs an electric signal in accordancewith the amount of the driver's depression of an accelerator pedal 14 todetect the engine load, a crank position sensor 16 that detects theengine rotation speed, and a cooling water temperature sensor 17 thatdetects the temperature of cooling water of the internal combustionengine 1 are connected to the ECU 20 via electric wiring, so that theoutput signals of these various sensors are input to the ECU 20.Furthermore, the first throttle 6, the second throttle 9, thelow-pressure EGR valve 32 and the high-pressure EGR valve 42 areconnected to the ECU 20 via electric wiring. The ECU 20 controls theseappliances and the like.

In this embodiment, the ECU 20 performs a clogging determination on thefilter 10. If the ECU 20 determines that the filter 10 is clogged, theECU 20 performs a restoration process of the filter 10. When performingthe clogging determination on the filter 10, the ECU 20 fixes thelow-pressure EGR valve 32 to a fully closed state. When the degree ofopening of the low-pressure EGR valve 32 is fixed to the fully closedstate, the amount of flow of exhaust passing through the filter 10 caneasily be estimated on the basis of the intake air amount detected bythe air flow meter 7. Therefore, the accuracy of the cloggingdetermination can be improved.

In this embodiment, the clogging determination on the filter 10 isperformed as follows. Herein, the cross-sectional area of the exhaustpipe 4 immediately upstream of the filter 10 is represented by A0, andthe flow speed of exhaust therein is represented by U0. Besides, theclogging of the filter 10 with PM is considered as throttling, and thecross-sectional area of the filter 10 is represented by A1, and the flowspeed of exhaust in the filter 10 is represented by Ucat.

If the foregoing relationship is applied to the Bernoulli theorem,Equation 1 can be obtained.

ρU ₀ ²/2+P ₀ =ρU _(cat) ²/2+P ₁  Equation 1

In the equation, P0 is the pressure of exhaust immediately upstream ofthe filter 10, and P1 is the pressure of exhaust immediately downstreamof the filter 10. It is assumed that the liquid density ρ is constant.Since the relationship of Equation 2 holds between the flow speed ofexhaust and the cross-sectional area, the differential pressure ΔPbetween the upstream side and the downstream side of the filter 10(hereinafter, referred to as “across-filter differential pressure”) canbe expressed as in Equation 3.

$\begin{matrix}{{U_{0}A_{0}} = {U_{cat}A_{1}}} & {{Equation}\mspace{14mu} 2} \\\begin{matrix}{{\Delta \; P} = \left( {P_{0} - P_{1}} \right)} \\{= {{\rho \; {U_{cat}^{2}/2}} - {\rho \; {U_{0}^{2}/2}}}} \\{= {{p\; {U_{cat}^{2}/2}} - {\rho \; {{U_{cat}^{2}\left( {A_{1}/A_{0}} \right)}^{2}/2}}}}\end{matrix} & {{Equation}\mspace{14mu} 3}\end{matrix}$

Then, Equation 3 can be re-written as Equation 4.

ΔP/U _(cat) ²=ρ(1−(A ₁ /A ₀)²)/2  Equation 4

In this equation, ΔP/Ucat² is a value that correlates with the degree ofclogging of the filter 10.

In this embodiment, if the ΔP/Ucat² is greater than a predeterminedvalue R1, the ECU 20 determines that the filter 10 is clogged, and thencarries out the restoration process of the filter 10.

The flow of the clogging determination on the filter 10 in thisembodiment will next be described. FIG. 2 is a flowchart showing theflow of the clogging determination on the filter 10 according to thisembodiment. The routine of this flowchart is repeatedly executed atevery predetermined time.

In step S101, it is determined whether or not a condition fordetermining the presence of the clogging of a filter 10 is met. In thisstep, it is determined whether or not a state suitable to perform theclogging determination on the filter 10 has been assumed. For example,it is determined whether or not the internal combustion engine 1 is in asteady state, or whether or not the temperature of the filter 10 is in apredetermined range. It is also allowable to determine whether or notthe vehicle has traveled such a predetermined distance that PM candeposit to a large amount. If an affirmative determination is made instep S101, the process proceeds to step S102. On the other hand, if anegative determination is made, the routine is ended.

In step S102, the ECU 20 controls the low-pressure EGR valve 32 to thefully closed state. That is, the ECU 20 controls the valve 32 so thatthe exhaust passing through the filter 10 will not contain thelow-pressure EGR gas. This facilitates the calculation of the amount offlow of exhaust passing through the filter 10.

In step S103, the air flow meter 7 detects a fresh air amount Ga.

In step S104, the differential pressure sensor 11 detects theacross-filter differential pressure ΔP.

In step S105, the exhaust temperature sensor 12 detects the temperatureof the exhaust passing through the filter 10 (hereinafter, referred toas “filter-passing exhaust temperature”) Tcat. The filter-passingexhaust temperature is used to convert the mass flow of exhaust passingthrough the filter 10 into a volume flow.

In step S106, the ECU 20 calculates the fuel injection amount Gf. Thefuel injection amount Gf is the amount of fuel injected into thecylinders 2, and is calculated on the basis of the engine rotationspeed, the engine load, etc.

In step S107, the exhaust pressure sensor 13 detects the pressure P6 inthe exhaust pipe 4 upstream of the filter 10 (hereinafter, referred toas “filter upstream-side pressure”).

In step S108, the ECU 20 calculates the volume flow Vcat of exhaustpassing through the filter 10. The volume flow Vcat can be obtainedthrough the following equation (equation of state of gas). In theequation, R is the gas constant.

V _(cat)=(G _(a) +G _(f))·R·T _(cat) /P ₆  Equation 5

In this embodiment the ECU 20 that finds the volume flow Vcatcorresponds to exhaust flow calculation means.

In step S109, the ECU 20 calculates a mean flow speed Ucat of exhaustpassing through the filter 10 (hereinafter, referred to as “mean exhaustflow speed”). The mean exhaust flow speed Ucat is calculated by dividingthe volume flow Vcat calculated in step S108 by the cross-sectional areaA of the filter 10. The cross-sectional area A of the filter 10 is foundbeforehand.

In step S110, the ECU 20 determines whether or not ΔP/Ucat² is greaterthan the predetermined value R1. As mentioned above, ΔP/Ucat² has acorrelation with the degree of clogging of the filter 10. Thepredetermined value R1 is found beforehand through experiments or thelike, as a lower limit value of the value at the time of occurrence ofthe clogging of the filter 10. If an affirmative determination is madein step S110, the process proceeds to step S111. On the other hand, if anegative determination is made, the process proceeds to step S112.

In this embodiment, the ECU 20 performing the process of step S110corresponds to clogging determination means in the invention.

In step S111, the ECU 20 requests a control for performing therestoration process of the filter 10. For example, the ECU 20 sets arestoration process control request flag to 1. This restoration processcontrol request flag is set to 1 when there is a need to perform therestoration process of the filter 10, and is set to 0 when there is noneed to perform the restoration process of the filter 10.

In step S112, the ECU 20 resets the request for the control forperforming the restoration process of the filter 10. For example, therestoration process control request flag is set to 0.

Thus, since the ECU 20 controls the low-pressure EGR valve 32 to thefully closed state at the time of determining whether the filter 10 isclogged, the clogging determination on the filter 10 can be moreaccurately performed. Although in this embodiment the ECU 20 controlsthe low-pressure EGR valve 32 to the fully closed state at the time ofdetermining whether the filter 10 is clogged, the degree of opening ofthe low-pressure EGR valve 32 may instead be controlled to a fixeddegree of opening that is other than the fully closed state. In thiscase, the amount of low-pressure EGR gas flowing through thelow-pressure EGR passageway 31 is directly measured or is estimated.Then, the amount of low-pressure EGR gas and the fresh air amountdetected by the air flow meter 7 are combined to calculate the amount offlow of exhaust passing through the filter 10.

Furthermore, in the case where the low-pressure EGR device 30 is notprovided but, for example, a system for supplying secondary air to thefilter 10 is provided, the supply of secondary air may be stopped whenthe clogging determination on the filter 10 is performed. Besides, theamount of supply of secondary air may be constant.

ii. Second Embodiment

In this embodiment, the EGR gas amount supplied into the cylinders 2 iskept constant by supplying an amount of high-pressure EGR gas thatcorresponds to the amount of decrease of the low-pressure EGR gas.

It is to be noted herein that when the degree of opening of thelow-pressure EGR valve 32 is changed, the ER gas amount supplied intothe cylinders 2 changes. For example, when the low-pressure EGR valve 32is controlled to the fully closed state in first embodiment, the supplyof the low-pressure EGR gas into the cylinders 2 discontinues.Therefore, there is possibility of lack of the EGR gas in the cylinders.

In second embodiment, on the other hand, the degree of opening of thehigh-pressure EGR valve 42 is controlled so that the EGR gas amountsupplied into the cylinders 2 is constant. In reality, the degree ofopening of the high-pressure EGR valve 42 is controlled so that theintake air amount is constant. What is taken into the cylinders 2includes fresh air and EGR gas. If the state of operation of theinternal combustion engine 1 does not change, the amount of fresh airand EGR gas combined does not change. Therefore, the EGR gas amount andthe fresh air amount have a relationship in which, for example, if theEGR gas amount decreases, the fresh air amount increases. That is, theEGR gas amount can be kept constant by controlling the degree of openingof the high-pressure EGR valve 42 so that the amount of fresh air, thatis, the intake air amount measured by the air flow meter 7, is constant.

FIG. 3 is a flowchart showing the flow of the clogging determination onthe filter 10 in accordance with this embodiment. The routine of thisflowchart is repeatedly executed at every predetermined time. The stepsof executing the same processes as those executed in the routine shownin the flowchart of FIG. 2 are affixed with the same referencecharacters, and the description thereof will be omitted.

In step S201, the ECU 20 calculates a target fresh air amount Gat. Thetarget fresh air amount Gat is calculated on the basis of the rotationspeed and the load of the internal combustion engine 1. The relationshipbetween the target fresh air amount Gat and the engine rotation speedand the engine load is found and presented in the form of a mapbeforehand through experiments or the like, and is stored in the ECU 20.

In step S202, the ECU 20 controls the degree of opening of thehigh-pressure EGR valve 42. The degree of opening of the high-pressureEGR valve 42 is feedback-controlled so that the fresh air amount Gadetected in step S103 equals the target fresh air amount Gat calculatedin step S201. It is to be noted herein that the ECU 20 controls thedegree of opening of the high-pressure EGR valve 42 in the increasingdirection if the ECU 20 controls the degree of opening of thelow-pressure EGR valve 32 in the decreasing direction.

Since the high-pressure EGR gas through the high-pressure EGR passageway41 flows from the exhaust pipe 4 upstream of the filter 10 to the intakepipe 3 downstream of the air flow meter 7, the high-pressure EGR gas hassubstantially no influence on the relationship between the fresh airamount and the amount of flow of exhaust passing through the filter 10.Therefore, at the time of the clogging determination on the filter 10,it is not necessary to take the high-pressure EGR gas amount intoaccount.

In this manner, if the degree of opening of the low-pressure EGR valve32 is changed while the ECU 20 performing the clogging determination onthe filter 10, the degree of opening of the high-pressure EGR valve 42is correspondingly changed, so that the EGR gas amount supplied into thecylinders 2 can be kept constant. This makes it possible to restrain thegeneration of NOx or the like while the ECU 20 is performing theclogging determination on the filter 10.

iii. Third Embodiment

In this embodiment, while the degree of opening of the low-pressure EGRvalve 32 is changing with the elapse of time, the low-pressure EGR gasamount at the current degree of opening is estimated. By adding thecurrent intake air amount measured by the air flow meter 7 to theestimated value, the amount of flow of exhaust passing through thefilter 10 with the current degree of opening is calculated.Specifically, the sum of the low-pressure EGR gas amount and the freshair amount is equal to the amount of flow of exhaust passing through thefilter 10. Therefore, even while the degree of opening of thelow-pressure EGR valve 32 is changing with the elapse of time, theamount of flow of exhaust passing through the filter 10 with the currentdegree of opening can be calculated by estimating the low-pressure EGRgas amount that corresponds to the degree of opening and detecting thefresh air amount provided at the time of that degree of opening.Incidentally, the amount of flow of the low-pressure EGR gas isestimated from the differential pressure between the upstream side andthe downstream side of the low-pressure EGR valve 32, the degree ofopening of the low-pressure EGR valve 32, etc.

FIGS. 4 and 5 are a flowchart showing the flow of the cloggingdetermination on the filter 10 in accordance with this embodiment. Theroutine of this flowchart is repeatedly executed at every predeterminedtime. The steps of executing the same processes as those executed in theroutine shown in the flowchart of FIG. 2 are affixed with the samereference characters, and the description thereof will be omitted.

In step S301, the cooling water temperature sensor 17 detects thetemperature of the cooling water of the internal combustion engine 1.

In step S302, the ECU 20 calculates the cooling efficiency of the EGRcooler 33. The cooling efficiency of the EGR cooler 33 has a correlationwith the cooling water temperature. Therefore, for example, arelationship between the cooling water temperature and the coolingefficiency of the EGR cooler 33 is found and presented in a mapbeforehand through experiments or the like, and is stored in the ECU 20.By substituting the cooling water temperature found in step S301 in thismap, the cooling efficiency of the EGR cooler 33 can be obtained.

In step S303, the density of the low-pressure EGR gas is calculated. Ifthe pressure and the temperature of the low-pressure EGR gas are known,the density of the low-pressure EGR gas is obtained by substituting thepressure and temperature values in the equation of state (equation ofstate of gas).

The temperature of the low-pressure EGR gas can be calculated, forexample, on the basis of the exhaust temperature T7 detected by theexhaust temperature sensor 12, the cooling efficiency of the EGR cooler33 and the amount of temperature drop that occurs when the low-pressureEGR gas flows through the low-pressure EGR passageway 31. Theserelationships may be found beforehand through experiments or the like.Furthermore, the temperature of the low-pressure EGR gas may also befound, for example, by using a sensor.

Furthermore, the pressure of the low-pressure EGR gas is detected, forexample, by a pressure sensor attached to the low-pressure EGRpassageway 31. Besides, the pressure in the intake pipe 3 connected tothe low-pressure EGR passageway 31 and the pressure of the low-pressureEGR gas may be equal. The temperature and the pressure may be estimatedfrom other sensors, or the state of operation of the internal combustionengine 1.

In step S304, the differential pressure between the upstream side andthe downstream side of the low-pressure EGR valve 32 (hereinafter,referred to as “across-low-pressure EGR valve differential pressure”) isdetected. The across-low-pressure EGR valve differential pressure can beobtained by, for example, using a differential pressure sensor that isattached to the low-pressure EGR passageway 31 so as to detect thedifferential pressure between the upstream side and the downstream sideof the low-pressure EGR valve 32.

In step S305, the ECU 20 calculates the opening area of the low-pressureEGR valve 32. For example, the relationship between the opening area andthe command value when the ECU 20 controls the degree of opening of thelow-pressure EGR valve 32 is found and presented in a map beforehand.Then, by substituting a command value, the opening area can be obtained.

In step S306, the ECU 20 calculates the amount of low-pressure EGR gasVegr passing through the low-pressure EGR valve 32.

Equation 4 is converted as in the following equation.

Ucat=√{square root over (2ΔP/(ρ(1−(A ₁ /A ₀)²)))}  Equation 6

Then, by replacing Ucat with the flow speed Uegr of the low-pressure EGRgas, and replacing the A1 with the opening area Aegr of the low-pressureEGR valve 32, the following equation can be obtained.

Uegr=√{square root over (2ΔP _(egr)/ρ_(egr))}×√{square root over(1/(1−(A _(egr) /A ₀)²))}  Equation 7

The amount Vegr of low-pressure EGR gas passing through the low-pressureEGR valve 32 can be obtained as in Equation 8.

$\begin{matrix}\begin{matrix}{V_{egr} = {U_{egr}A_{egr}}} \\{= {A_{0}A_{egr}\sqrt{2\; \Delta \; {P_{egr}/\left( {\rho_{egr}\left( {A_{0}^{2} - A_{egr}^{2}} \right)} \right)}}}}\end{matrix} & {{Equation}\mspace{14mu} 8}\end{matrix}$

In this embodiment, the ECU 20 calculating the amount Vegr oflow-pressure EGR gas corresponds to EGR gas amount detection means.

In step S307, the ECU 20 calculates the amount Vcat of flow of exhaustpassing through the filter 10. The amount Vcat of flow of exhaust iscalculated through Equation 9 as a value obtained by summing the amountof flow of low-pressure EGR gas passing through the low-pressure EGRvalve 32, and the amount of flow of fresh air.

V _(cat) =V _(egr)+(G _(a) +G _(f))·R·T _(cat) /P ₆  Equation 9

Thus, even in the case where the low-pressure EGR valve 32 is at adegree of opening other than the fully closed state and is changing withthe elapse of time, the amount of flow of exhaust passing through thefilter 10 can be found in accordance with the degree of opening of thelow-pressure EGR valve 32, so that the clogging determination on thefilter 10 can be performed in a wider range of the state of operation.

1.-9. (canceled)
 10. An exhaust purification device of an internalcombustion engine, comprising: a particulate filter that is provided inan exhaust passageway and that traps a particulate matter in exhaust; anintake air amount detection portion that detects an amount of fresh airflowing in an intake passageway; a gas supply portion that supplies agas to the intake passageway that is on a downstream side of the intakeair amount detection portion and on an upstream side of the particulatefilter; an exhaust flow calculation portion that calculates an amount offlow of exhaust passing through the particulate filter based on theamount of the gas supplied and the amount of fresh air detected; adifferential pressure detection portion that detects a differentialpressure between the upstream side and the downstream side of theparticulate filter in the exhaust passageway; and a cloggingdetermination portion that determines whether the particulate filter isclogged based on the amount of flow of exhaust calculated and thedifferential pressure detected; a turbocharger that has a turbine in theexhaust passageway, and a compressor in the intake passageway, ahigh-pressure EGR passageway that connects the exhaust passagewayupstream of the particulate filter and the intake passageway downstreamof the intake air amount detection portion; and a high-pressure EGRvalve that changes the passageway cross-sectional area of thehigh-pressure EGR passageway; wherein the gas supply portion is an EGRdevice that has an EGR passageway that connects the exhaust passagewaydownstream of the particulate filter and the intake passagewaydownstream of the intake air amount detection portion, and an EGR valvethat is provided in the EGR passageway and that changes a passagewaycross-sectional area of the EGR passageway; wherein the amount of thegas supplied by the gas supply portion is the amount of an EGR gasdetected by EGR gas amount detection portion for detecting the amount ofthe EGR gas flowing in the EGR passageway; wherein the EGR passageway isa low-pressure EGR passageway that connects the exhaust passagewaydownstream of the turbine and the intake passageway upstream of thecompressor; wherein when it is determined by the clogging determinationportion whether the particulate filter is clogged, the degree of openingof the EGR valve is made smaller than when it is not determined whetherthe particulate filter is clogged, and the EGR gas amount flowing in thehigh-pressure EGR passageway is changed by the high-pressure EGR valveso that the EGR gas amount supplied into a cylinder of the internalcombustion engine is constant.
 11. The exhaust purification device ofthe internal combustion engine according to claim 10, wherein theclogging determination portion estimates an amount of the particulatematter trapped on the particulate filter.
 12. The exhaust purificationdevice of the internal combustion engine according to claim 10, whereinthe EGR gas amount detection portion detects the amount of flow of gasin the low-pressure EGR passageway from at least the differentialpressure between the passageway on the upstream side of the EGR valveand the passageway on the downstream side of the EGR valve, and a degreeof opening of the EGR valve.
 13. The exhaust purification device of theinternal combustion engine according to claim 10, wherein when theclogging determination portion determines whether the particulate filteris clogged, the degree of opening of the EGR valve is fixed.
 14. Theexhaust purification device of the internal combustion engine accordingto claim 13, wherein the degree of opening of the EGR valve is fixed toa fully closed state when it is determined by the clogging determinationportion whether the particulate filter is clogged.
 15. The exhaustpurification device of the internal combustion engine according to claim10, wherein when it is determined by the clogging determination portionwhether the particulate filter is clogged, the degree of opening of theEGR valve is set to a degree of opening that is not the fully closedstate, and the exhaust flow calculation portion estimates the amount offlow of exhaust passing through the particulate filter based on theamount of fresh air detected by the intake air amount detection portionand the amount of the EGR gas detected by the EGR gas amount detectionportion, and the clogging determination portion determines whether theparticulate filter is clogged based on the amount of flow of exhaustestimated by the exhaust flow calculation portion and the differentialpressure detected by the differential pressure detection portion. 16.The exhaust purification device of the internal combustion engineaccording to claim 10, wherein determination by the cloggingdetermination portion as to whether the particulate filter is clogged isperformed when at least one of (i) a condition that the internalcombustion engine is in a steady state, (ii) a condition thattemperature of the particulate filter is within a predetermined range,and (iii) a condition that the vehicle has traveled a predetermineddistance, is met.
 17. A control method of an exhaust purification deviceof an internal combustion engine which includes: a particulate filterthat is provided in an exhaust passageway and that traps a particulatematter in exhaust; an intake air amount detection portion that detectsan amount of fresh air flowing in an intake passageway; a gas supplyportion that supplies a gas to the intake passageway that is on adownstream side of the intake air amount detection portion and on anupstream side of the particulate filter; a differential pressuredetection portion that detects a differential pressure between theupstream side and the downstream side of the particulate filter in theexhaust passageway; a turbocharger that has a turbine in the exhaustpassageway, and a compressor in the intake passageway; a high-pressureEGR passageway that connects the exhaust passageway upstream of theparticulate filter and the intake passageway downstream of the intakeair amount detection portion; and a high-pressure EGR valve that changesthe passageway cross-sectional area of the high-pressure EGR passageway;wherein the EGR passageway is a low-pressure EGR passageway thatconnects the exhaust passageway downstream of the turbine and the intakepassageway upstream of the compressor; the control method comprising:calculating an amount of flow of exhaust passing through the particulatefilter based on the amount of the gas supplied and the amount of freshair detected; and determining whether the particulate filter is cloggedbased on the amount of flow of exhaust calculated and the differentialpressure detected; wherein: the gas supply portion is an EGR device thathas an EGR passageway that connects the exhaust passageway downstream ofthe particulate filter and the intake passageway downstream of theintake air amount detection portion, an EGR valve that is provided inthe EGR passageway and that changes a passageway cross-sectional area ofthe EGR passageway; the amount of the gas supplied by the gas supplyportion is the amount of an EGR gas detected by EGR gas amount detectionportion that detects the amount of the EGR gas flowing in the EGRpassageway; and when it is determined by the clogging determinationportion whether the particulate filter is clogged, the degree of openingof the EGR valve is made smaller than when it is not determined whetherthe particulate filter is clogged, and the EGR gas amount flowing in thehigh-pressure EGR passageway is changed by the high-pressure EGR valveso that the EGR gas amount supplied into a cylinder of the internalcombustion engine is constant.